Something that you are required to do by every single venue that offers a service in order to participate is not really what I would call opt in. Yes, you can opt out by never going to a nightclub, but that seems different.

You can’t really call something opt-in if opting out means that you are barred from participating in an entire class of activity unrelated to what you opted out of.

As a counter example, the TSA in the US is now starting to use facial scans for ID, but you can opt out by telling the agent. It does not mean that you cannot go flying, it means that they use a human to identify you without the use of computerized facial scans.